Valve drive system of an internal combustion engine

ABSTRACT

A valve drive system of an internal combustion engine provided with a camshaft (20) adapted to be rotated by means of a crankshaft, a cam robe (38) rotatably mounted on the camshaft (20), a cam (24) formed integrally with the cam robe (38) and serving to open and close an intake valve (24) in cooperation with a valve spring (92), a viscous coupling (40) arranged between the camshaft (20) and the cam robe (38) and serving to transmit a rotatory force of the camshaft (20) to the cam robe (38), and a spiral spring (42) for connecting the camshaft (20) and the cam robe (38) and urging the cam robe (38) toward a predetermined rotational angle position with respect to the camshaft (20) .

TECHNICAL FIELD

The present invention relates to a valve drive system for opening andclosing an intake valve or an exhaust valve of an internal combustionengine, and more particularly, to a valve drive system having therein amechanism for varying a valve timing.

BACKGROUND ART

Valve drive systems having a variable valve timing mechanism therein aredisclosed in, for example, Jpn. Pat. Appln. KOKAI Publication Nos.59-54713 and 59-110816. These conventional systems comprise a camrotatably mounted on a camshaft; and a connecting device for connectingthe camshaft and the cam and adjusting a rotational phase of the camwith respect to the camshaft. This connecting device includes a pressurechamber for hydraulically connecting the camshaft and the cam, and ahydraulic circuit for adjusting a hydraulic pressure in the pressurechamber in accordance with the operation state of an internal combustionengine, and the rotational phase of the cam with respect to the camshaftis adjusted by means of the pressure in the pressure chamber.

In the case of the connecting device described above, accurate controlof the rotational phase of the cam with respect to the camshaft, thatis, valve timing, entails fine control of the pressure in the pressurechamber by means of a solenoid-controlled valve in the hydrauliccircuit. Moreover, the hydraulic circuit requires use of a hydraulicpump, as a hydraulic pressure source, for generating a high hydraulicpressure, and oil leakage from the hydraulic circuit must be preventedsecurely. Consequently, components of the connecting device requirehigh-accuracy machining, and the number of components of the connectingdevice increases.

The object of the present invention is to provide a valve drive systemof a simple construction, capable of varying a timing for opening orclosing a valve without requiring an electronic control, and improvingthe output of an internal combustion engine throughout an operationalregion of the internal combustion engine.

SUMMARY OF THE INVENTION

The above object is achieved by a valve drive system of the presentinvention. The valve drive system of the present invention comprises, afirst rotating member adapted to be rotated in association with acrankshaft of an internal combustion engine, a second rotating memberrotatably provided with respect to the first rotating member, a camprovided for the second rotating member and adapted to cooperate withone valve of intake and exhaust valves, and connecting means forconnecting the first rotating member and the second rotating member toallow the first and second rotating members to relatively rotate eachother. This connecting means has a transmission function to transmit therotatory force of the first rotating member to the second rotatingmember, thereby causing the cam to rotate together with the secondrotating member. The connecting means also has a variable function torestrict an increase of the rotating speed of the second rotating memberbased on the restoring force of a valve spring of the valve inaccordance with the operation state of the internal combustion engine,in a process of reducing the cam lift as the cam rotates, and settle thetime of termination of the cam lift with respect to the rotational phaseof the crankshaft.

According to the valve drive system, as described above, the speed ofrotation of the second rotating member relative to the first rotatingmember is increased by means of the valve spring in the process ofreducing the cam lift. However, this increase of the speed of rotationis restricted by the variable function of the connecting means dependingon the operation state of the internal combustion engine, whereby thetime of termination of the cam lift, that is, valve closing timing, iscontrolled.

The transmission and variable functions of the connecting means can beeffectuated by means of a fluid coupling which connects the first andsecond rotating members.

If the second rotating member has a hollow shape, the relative rotationof the first and second rotating members can be allowed by onlyrotatably mounting the second rotating member on the first rotatingmember.

In the case where the valve drive system of the present invention isapplied to a multicylinder engine, the system can comprise a firstrotating member common to the individual cylinders, and second rotatingmembers provided individually for the cylinders.

The connecting means of the valve drive system of the present inventioncan further include a pusher portion provided for the first rotatingmember, and a receiving portion provided for the second rotating memberand adapted to engage the pusher portion in the process of increasingthe cam lift. Preferably, in this case, the connecting means should beprovided with urging means for the first and second rotating members,and this urging means urges the first and second rotating members sothat the pusher portion abuts against the receiving portion.

The connecting means, which is provided with the pusher portion and thereceiving portion, as described above, causes the first and secondrotating members to rotate integrally with each other in the process ofincreasing the cam lift, so that the valve opening timing is settled inaccordance with a profile of the cam.

A viscous coupling can be used as the fluid coupling of the connectingmeans. The viscous coupling includes a fluid chamber defined between thefirst and second rotating members and having a viscous fluid sealedtherein, a first plate located in the fluid chamber and fixed to thefirst rotating member, and a second plate located opposite the firstplate in the fluid chamber and fixed to the second rotating member.

Since the bonding force between the first and second plates variesdepending on the rotating speed of the first rotating member, theaforesaid viscous coupling can simultaneously fulfill the aforementionedtransmission function and variable function of the connecting means, andcan control the valve opening timing and valve closing timing withoutusing an electronic control.

If the second rotating member includes a first portion fitted on thefirst rotating member from the outside and a second portion having adiameter larger than that of the first portion, this second portion canbe used as part of a casing which defines the aforesaid fluid chamber ofthe viscous coupling. Preferably, in this case, the second rotatingmember should have the second portion at one end portion thereof and theaforesaid receiving portion at the other end portion thereof.

The fluid coupling of the connecting means is not limited to the viscouscoupling, as described above, and may alternatively be formed of a fluidcoupling. The fluid coupling includes a chamber defined between thefirst and second rotating members and having a noncompressive fluidsealed therein, a wall member attached to the first rotating member anddividing the chamber into first and second fluid chambers in therotating direction of the first and second rotating members, and acommunication channel connecting the first and second fluid chambers.Preferably, the fluid coupling further includes adjusting means forchanging the flow resistance of the communication channel.

According to this fluid coupling, the aforementioned transmissionfunction and variable function are fulfilled as the characteristic ofthe delivery of the noncompressive fluid between the first and secondfluid chambers varies depending on the rotating speed of the firstrotating member, and the valve opening timing and valve closing timingcan be controlled in accordance with the operation state of the internalcombustion engine without using electronic control.

The fluid coupling of the connecting means is expected to fulfill itstransmission function only in the process of increasing the cam lift.

The connecting means can further include urging means for urging thesecond rotating member toward the first rotating member. The urgingmeans settles the rotational angle position of the second rotatingmember with respect to the first rotating member when the first rotatingmember and second rotating member rotate integrally with each other. Inthis case, the second rotating member can relatively rotate with respectto the first rotating member while resisting the urging force of theurging means.

Moreover, the connecting means can further include limiting means forlimiting an allowable range of relative rotation between the first andsecond rotating members.

The connecting means may be provided with a second fluid coupling of atype different from that of the aforesaid first fluid coupling. Thesecond fluid coupling includes a wall member attached to the firstrotating member and having a front face situated on the front side withrespect to the rotating direction of the first rotating member, a fluidchamber defined between the front face of the wall member and the secondrotating member, and control means for controlling the supply to anddischarge of a noncompressive fluid from the fluid chamber. In thiscase, the control means can include means for limiting the speed ofdischarge of the noncompressive fluid from the fluid chamber. The secondfluid coupling fulfills the same function as the first fluid coupling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a valve drive system according to a firstembodiment applied to an internal combustion engine;

FIG. 2 is a sectional view of the system of FIG. 1;

FIG. 3 is a plan view showing an inner plate of a viscous coupling ofFIG. 1;

FIG. 4 is a front view of a spiral spring for connecting a cam robe andan inner sleeve;

FIG. 5 is a longitudinal sectional view of the system of FIG. 1;

FIG. 6 is a graph showing valve lift characteristics based on the systemof FIG. 1;

FIG. 7 is a graph showing an advanced angle of the valve closing timingcompared with the engine speed;

FIG. 8 is a graph showing an advanced angle of the valve closing timingcompared with the oil viscosity ratio of the viscous coupling;

FIG. 9 is a graph showing an advanced angle of the valve opening timingcompared with the spring constant ratio of the spiral spring;

FIG. 10 is a graph showing valve lift characteristics of intake andexhaust valves compared with the crank angle;

FIG. 11 is a plan view showing a valve drive system according to asecond embodiment;

FIG. 12 is a side view of a cam robe of the system of FIG. 11;

FIG. 13 is a sectional view of the cam robe of FIG. 12;

FIG. 14 is a front view of the cam robe of FIG. 12;

FIG. 15 is a rear view of the cam robe of FIG. 12;

FIG. 16 is a side view of a cam robe applied to a cylinder #1 of theinternal combustion engine of FIG. 11;

FIG. 17 is a graph showing valve lift characteristics based on thesystem of FIG. 11;

FIG. 18 is a graph showing valve lift characteristics of intake andexhaust valves compared with the crank angle;

FIG. 19 is a sectional view showing a valve drive system according to athird embodiment;

FIG. 20 is a longitudinal sectional view showing part of a valve drivesystem according to a fourth embodiment;

FIG. 21 is a cross-sectional view showing part of the system of FIG. 20;

FIG. 22 is a view showing a spiral spring shown in FIG. 20;

FIG. 23 is a cross-sectional view showing a state where a cam robe inthe state of FIG. 21 is relatively rotated to a camshaft;

FIG. 24 is a graph showing valve lift characteristics of an intake valvebased on the system of FIG. 20;

FIG. 25 is a cross-sectional view showing part of a valve drive systemaccording to a fifth embodiment;

FIG. 26 is a graph showing valve lift characteristics of an intake valvebased on the system of FIG. 25;

FIG. 27 is a graph showing the valve-open period of an intake valvecompared with the engine speed in the system of FIG. 25;

FIG. 28 is a sectional view showing part of a valve drive systemaccording to a sixth embodiment;

FIG. 29 is a cross-sectional view of the system of FIG. 28;

FIG. 30 is an enlarged view showing part of the system of FIG. 28;

FIG. 31 is a cross-sectional view showing a state where a cam robe inthe state of FIG. 29 is relatively rotated to a camshaft;

FIG. 32 is a cross-sectional view showing part of a valve drive systemaccording to a seventh embodiment;

FIG. 33 is an enlarged view showing part of a valve drive systemaccording to an eighth embodiment;

FIG. 34 is a view showing a state where a variable orifice of FIG. 33 isactuated;

FIG. 35 is a graph showing the opening of the variable orifice comparedwith the distance of movement of a piston of FIG. 33;

FIG. 36 is an enlarged sectional view showing part of a valve drivesystem according to a ninth embodiment; and

FIG. 37 is a cross-sectional view showing part of a valve drive systemaccording to a tenth embodiment.

BEST MODE OF CARRYING OUT THE INVENTION

Referring to FIG. 1, there is shown a four-cylinder gasoline engine(hereinafter referred to simply as "engine") 10. Each cylinder of theengine 10 is furnished with four valves. A cylinder head 12 of theengine 10 is mounted on a cylinder block (not shown), and this cylinderblock is provided with a crankshaft (not shown). The rotatory force ofthe crankshaft is transmitted to timing gears 16 and 18 by means of atiming belt 14. These timing gears 16 and 18 are mounted, respectively,on first ends of camshafts 20 and 22 for use as first rotating members,and rotate integrally with these camshafts 20 and 22. Here the camshafts20 and 22 are rotated at a rotational frequency half that of thecrankshaft. The camshaft 20 is fitted with a plurality of intake cams26, while the camshaft 22 is fitted with a plurality of exhaust cams 26.The intake cams 24 and the exhaust cams 26 are arranged in a pair foreach cylinder.

The camshafts 20 and 22 extend parallel to each other along thelongitudinal axis of the cylinder head 12, and the opposite end portionsof these camshafts 20 and 22 are rotatably supported on the cylinderhead 12 by means of end bearings 28, individually.

The camshaft 20 of the aforementioned valve drive system is providedwith variable valve timing devices 30 in regions situated abovecylinders #1 to #4, individually, and the camshaft 22 is also providedwith variable valve timing devices 32 in regions situated above thecylinders #1 to #4, individually.

Since these variable valve timing devices 30 and 32 according to a firstembodiment have the same construction, the device 30 for the cylinder #1will now be described with reference to FIG. 2.

Broadly, the variable valve timing device 30 includes an inner sleeve 36mounted on the camshaft 20 by means of a semilunar key 34, a cylindricalcam robe 38, surrounding the camshaft 20, for use as a second rotatingmember, a viscous coupling 40 interposed between the cam robe 38 and theinner sleeve 36, and a spiral spring 42 interposed between the cam robe38 and the inner sleeve 36.

The inner sleeve 36 has a boss and a flange 44. The flange 44 is formedintegrally on the outer peripheral surface of the boss. This flange 44divides the boss of the inner sleeve 36 between an inside boss portionand an outside boss portion

The cam robe 38 includes a large-diameter cylindrical portion 50 whichcovers the whole inner sleeve 36, and a small-diameter cylindricalportion 54 which is mounted on the camshaft 20 by means of a metalbearing 52. A neck portion 56 is formed on the central portion of theouter peripheral surface of the small-diameter cylindrical portion 54.The neck portion 56 is rotatably supported on the cylinder head 12 bymeans of a central bearing 58. This central bearing 58 includes a camjournal 60 which protrudes integrally from the cylinder head 12, and acam cap 62. The neck portion 56 is held between the cam journal 60 andthe cam cap 62. The cam cap 62 is fitted on the neck portion 56 of thecam robe 38, and fixed to the cam journal 60 by means of a pair of bolts(not shown). Thus, the axial movement of the cam robe 38 is prevented bythe cam cap 62, and the cam cap 62 is used to position the cam robe 38with respect to the axial direction.

Ring-shaped seals 64 and 66 are located between the distal end portionof the inside boss portion 46 and the inner peripheral surface of thelarge-diameter cylindrical portion 50, and between the flange 44 and theinner peripheral surface of the large-diameter cylindrical portion 50,respectively. These seals 64 and 66 liquid-tightly keep an oil chamber68 defined between the inner sleeve 36 and the cam robe 38 whileallowing relative rotation of these members. The oil chamber 68 isfilled with silicone oil which has a predetermined viscosity.

The viscous coupling 40 includes a plurality of inner plates and aplurality of outer plates. The inner plates are nonrotatably mounted onthe inside boss portion 46, while the outer plates are nonrotatablyattached to the large-diameter cylindrical portion 50. Morespecifically, the outer peripheral surface of the inside boss portion 46and the inner peripheral surface of the large-diameter cylindricalportion 50 are formed with splines 70 and 72, respectively. The innerperiphery of each inner plate is in engagement of the spline 70 of theinside boss portion 46, while the outer periphery of each outer plate isin engagement with the spline 72 of the large-diameter cylindricalportion 50.

As shown in FIG. 3, each of the inner plates 74 has a plurality of slits76, which are arranged at regular intervals in the circumferentialdirection of the inner plate 74. In FIG. 3, each of the slits 76 isinclined so that its inner end is situated closer to the center of theinner plate 74 as compared to its outer end with respect to the rotatingdirection of the camshaft 20 indicated by the arrow.

The aforesaid slits 76 may be provided in each of the outer plates inplace of the inner plates 74.

As shown in FIG. 4, the inner end of the spiral spring 42 is fixed tothe outer peripheral surface of the outside boss portion 48, while theouter end of the spiral spring 42 is fixed to an open end of thelarge-diameter cylindrical portion 50. Moreover, the spiral spring 42 iscovered by cup-shaped cover 78. An open end of the cover 78 is fixed tothe outer peripheral surface of the large-diameter cylindrical portion50.

The small-diameter cylindrical portion 54 of the cam robe 38 is formedintegrally with a pair of intake cams 24, and these intake cams 24 havethe same profile.

Referring to FIG. 5, there is shown a rocker arm 80 which cooperateswith the one intake cam 24. A roller 82 is rotatably supported on therocker arm 80 and this roller 82 is in rolling contact with the intakecam 24. One end of the rocker arm 80 is supported on a hydraulic lashadjuster 84 mounted on the cylinder head 12. The lash adjuster 84 servescontinually to remove a gap between a base circle face 24a of the intakecam 24 and the roller 82 on the rocker arm 80.

The other end of the rocker arm 80 abuts against the upper end of avalve stem of an intake valve 86. The intake valve 86 is subjected to anurging force of a valve spring 92 in the direction to close an intakeport 90 which opens into a combustion chamber 88, that is, upward as inFIG. 5.

When the intake cam 24 is rotated together with the camshaft 20, theintake cam 24 causes the intake valve 86 to vertically reciprocatethrough the medium of the rocker arm 80 and the valve spring 92,following its cam profile. Thus, the intake valve 86 opens the intakeport 90 cyclically.

A similar valve drive mechanism is also provided between the otherintake cam 24 of the cam robe 38 and its corresponding intake valve 86,and a pair of intake valves 86 of the cylinder #1 open and close theirrespective intake ports in synchronism with each other.

On the other hand, a pair of exhaust valves 94 (see FIG. 1) of thecylinder #1 are opened and closed by means of similar valve drivemechanism as the exhaust cam 26 is rotated together with the camshaft22.

The following is a description of the operation of the variable valvetiming device 30.

When the rotatory force of the camshaft 20 is transmitted from the innersleeve 36 to the cam robe 38 through the spiral spring 42 and theviscous coupling 40 as the camshaft 20 rotates, the cam robe 38 is alsorotated.

In the condition that the rotating speed of the engine 10 or thecamshaft 20 is in a low-speed rotation region, the transmission torqueof the viscous coupling 40, which is the bonding force between its innerand outer plates, is relatively low. In this region, the viscouscoupling 40 allows the inner sleeve 36 and the cam robe 38 to relativelyrotate to each other. When the rotating speed of the camshaft 20 is in ahigh-speed rotation region, on the other hand, the bonding force betweenthe inner and outer plates of the viscous coupling 40 increases, so thatthe viscous coupling 40 connects the inner sleeve 36 and the cam robe 38integrally to each other.

When a lift face 24b of the intake cam 24 which is continuous with thebase circle face 24a, depresses the rocker arm 80 through the medium ofthe roller 82 as the intake cam 24 rotates, the intake cam 24 issubjected to a reaction force from the roller 82 on the rocker arm 80due to the urging force of the valve spring 92. The line of action ofthis reaction force is opposite to a rotating direction Ro (see FIG. 5)of the intake cam 24. Thus, the intake cam 24 (outer plates of viscouscoupling 40) rotates with a delay with respect to the camshaft 20 (innerplates of viscous coupling 40). As a result, the speed of increase ofthe valve lift of the intake valve 86 is lower than in the case wherethe camshaft 20 and the intake cam 24 rotate integrally with each otherwhen the rotating speed of the engine 10 is in the high-speed rotationregion.

Referring to FIG. 6, there are shown valve lift characteristics of theintake valve 86. In FIG. 6, valve lift characteristics Hvh and Hvlindicated by a full line and a broken line represent the cases where therotating speed of the engine 10 is in the high-speed rotation region andthe low-speed rotation region, respectively. When the valve liftcharacteristics Hvh and Hvl are compared, the increasing speed of thevalve lift of the intake valve 86 is found to be lower in the low-speedrotation region than in the high-speed rotation region. As is evidentfrom the above description, this delay of the increasing speed of thevalve lift decreases as the rotating speed of the engine 10 increases.

After the intake valve 86 is lifted to open the intake port 90, the camrobe 38, which is formed integrally with the intake cam 24, rotates in amanner such that the spiral spring 42 is elastically deformed in awinding direction R1 (see FIG. 4). Thus, the rotational angular speed ofthe cam robe 38 becomes lower than the rotational angular speed of thecamshaft 20. As seen from the valve lift characteristic Hvl, indicatedby broken line in FIG. 6, the valve lift of the intake valve 86 issubject to a delay with respect to the valve lift obtained in thehigh-speed rotation region, and the speed of the valve lift is lowerthan the speed of the valve lift obtained in the high-speed rotationregion.

In connection with this, FIG. 6 also shows the change of the lift speedassociated with the valve lift of the intake valve 86. Lift speedcharacteristics Vh and V1 indicated by full line and broken linerepresent the cases where the rotating speed of the engine 10 is in thehigh-speed rotation region and the low-speed rotation region,respectively. When the lift speed characteristics Vh and V1 arecompared, it is seen that the rise of the valve opening speed of theintake valve 86 when the rotating speed of the engine 10 is in thelow-speed rotation region is slower than the rise of the valve openingspeed in the high-speed rotation region, and that the maximum valveopening speed in the low-speed rotation region is lower than the maximumvalve opening speed in the high-speed rotation region.

When a return face 24d of the intake cam 24 abuts the roller 83 of therocker arm 80, following a cam top 24c of the cam, after the rotation ofthe intake cam 24 is advanced so that the roller 83 is passed by thelift face 24b of the intake cam 24, the intake valve 84 is subjected tothe urging force of the valve spring 92, and moves in the valve closingdirection. In this case, the urging force of the valve spring 92, whichworks on the intake cam 24 via the rocker arm 80, acts in the rotatingdirection of the intake cam 24, and the intake cam 24 is also subjectedto the restoring force of the spiral spring 42 in its rotating directionthrough the cam robe 38. Thus, the rotation of the intake cam 24advances with respect to the camshaft 20, and the spiral spring 42 isrewound and restored to its original state.

As seen from the valve lift characteristic Hvl, as indicated by thebroken line in FIG. 6, the intake valve 86 closes the intake port 90earlier in the low-speed rotation region than in the high-speed rotationregion by an advanced angle A in terms of the rotational angle of theintake cam 24. As seen from the lift speed characteristic V1, asindicated by broken line in FIG. 6, moreover, the valve closing speed ofthe intake valve 86 in the low-speed rotation region becomes higher thanin the high-speed rotation region. As a result, a valve-open period Tvlof the intake valve 86 for the low-speed rotation region is made shorterthan a valve-open period Tvh for the high-speed rotation region.

As shown in FIG. 7, the advanced angle A increases to reach its maximumvalue Amax (e.g., 30°) as the rotating speed of the engine 10 lowers. InFIG. 7, E1 and E2 represent the low-speed rotation region and high-speedrotation region of the engine 1, respectively. Further, the advancedangle A can be adjusted in accordance with the viscosity of silicone oilin the viscous coupling 40 and the spring constant of the spiral spring42.

Referring to FIG. 8, the ratio of the viscosity of the silicone oil usedto the viscosity of silicone oil for reference and the advanced angle Aare represented by the axes of abscissa and ordinate, respectively. Asshown in FIG. 8, the advanced angle A is decreased as the viscosityratio increases.

Referring to FIG. 9, the ratio of the spring constant of the spiralspring used to the spring constant of a spiral spring for reference andthe advanced angle A are represented by the axes of abscissa andordinate, respectively. As shown in FIG. 9, the advanced angle A isdecreased as the spring constant ratio increases. FIG. 9 shows theresult of an experiment conducted with the rotating speed of thecamshaft 24 being constant(1,000 rpm).

While the base circle face 24a of the intake cam 24 is passing by theroller 82 on the rocker arm 80, the spiral spring 42 restores the intakecam 24 to its initial rotational angle position with respect to thecamshaft 20.

When the engine 10 or the camshaft 20 is in the high-speed rotationregion, the transmission torque of the viscous coupling 40, that is, thebonding force between its inner and outer plates, increases. As therotating speed of the camshaft 20 increases, consequently, the viscouscoupling 40 gradually ceases to allow the inner sleeve 36 and the camrobe 38 to relatively rotate to each other.

When the intake cam 24 depresses the roller 82 on the rocker arm 80 bymeans of its lift face 24b as the intake cam 24 rotates with therotating speed of the camshaft 20 in the high-speed rotation region, theintake cam 24 is subjected to the reaction force from the roller 82 onthe rocker arm 80, based on the urging force of the valve spring 92.This reaction force acts in the direction opposite to the rotatingdirection of the intake cam 24. In this case, however, the transmissiontorque of the viscous coupling 40 is so high that the starting timingfor the valve lift of the intake valve 86 is subject to only a smalldelay with respect to the start timing for the case where the intake cam24 is connected integrally to the camshaft 20. Thus, as seen from thevalve lift characteristic Hvh, as indicated by full line in FIG. 6, thestarting timing for the valve lift in the high-speed operation region isearlier than the starting timing in the case of the low-speed operationregion.

Even though the rotation of the intake cam 24 advances after the intakevalve 86 is lifted to open the intake port 90, relative rotation betweenthe intake cam 24 (cam robe 38) and the camshaft 20 (inner sleeve 36) isslight. Therefore, the elastic deformation of the spiral spring 42 isalso only slight, since the transmission torque of the viscous coupling40 is high.

In this case, the valve lift and lift speed of the intake valve 86change in accordance with the valve lift characteristic Hvh and the liftspeed characteristic Vh, as indicated by full lines in FIG. 6, and thevalve opening speed of the intake valve 86 is higher than in the casefor the low-speed operation region.

Even though the rotation of the intake cam 24 advances so that thereturn face 24d of the intake cam 24 reaches the surface of the roller82 on the rocker arm 80, the relative rotation between the intake cam 24and the cam robe 38 is also slight in this case, since the transmissiontorque of the viscous coupling 40 is high. Thus, the valve closing speedof the intake valve is substantially equal to the valve opening speed.

Since the transmission torque of the viscous coupling 40 is greater thanthe restoring force of the spiral spring 42 when the rotating speed ofthe camshaft 20 is in the medium or high-speed rotation region, it isdifficult for the intake cam 24 to return to its initial rotationalangle position with respect to the camshaft 20, and this return issubject to a delay. This delay will disturb the rise portion of thevalve lift characteristic of the intake valve 86. As mentioned before,however, each of inner plates 74 of the viscous coupling 40 has aplurality of slits 76 (see FIG. 3). When the intake cam 24 returns toits initial rotational angle position, the silicone oil in the viscouscoupling 40 is therefore centralized through the slits 76, so that thetransmission torque of the viscous coupling 40 is reduced. Thus, theintake cam 24 can quickly return to its initial rotational angleposition by means of the restoring force of the spiral spring 42.

The variable valve timing device 32 on the exhaust side of the cylinder#1 and the variable valve timing devices 30 and 32 for the cylinders #2to #4 operate in the same manner.

According to the engine 10 provided with the variable valve timingdevices 30 and 32 described above, valve-open periods Ti1 and Te1 of theintake and exhaust valves 86 and 94 become shorter than valve-openperiods which are settled depending on the cam profiles of the intakeand exhaust cams 24 and 26 when the rotating speed of the engine 10 isin the low-speed rotation region, as shown in FIG. 10. Thus, an overlapperiod To1 between the valve-open periods Ti1 and Te1 is shortened, sothat blow-by of the engine 10 or discharge of raw gas can be prevented.As a result, idling of the engine 10 can be stabilized, in particular.

When the rotating speed of the engine 10 is in the high-speed rotationregion, on the other hand, the force of inertia of intake air into theengine 10 is increased. In this case, since valve-open periods Ti2 andTe2 of the intake and exhaust valves 86 and 94 are longer than thevalve-open periods Ti1 and Te1 for the low-speed rotation region, asshown in FIG. 10, an overlap period To2 between these valve-open periodsTi2 and Te2 is also longer, so that supercharging efficiency of intakeair and exhaust efficiency can be improved individually.

Referring then to FIG. 11, there is shown an engine 10' which compriseswith variable valve timing devices 30' and 32' according to a secondembodiment. In the description of the engine 10' and the devices 30' and32', and in the description of other embodiments to follow, similarreference numerals are used to designate the members and parts whichhave the same functions as the members and parts in the variable valvetiming devices of the foregoing embodiment, and a description of thosemembers and parts will be omitted.

The variable valve timing devices 30' and 32', like those in the firstembodiment, are mounted on camshafts 20 and 22, respectively,corresponding to cylinders #1 to #4. The device 30' for the cylinder #2,among the devices 30' and 32', is shown in FIGS. 12 and 13.

The variable valve timing device 30' is further provided with a dogclutch 100 for restraining relative rotation between a cam robe 38 andthe camshaft 20. This dog clutch 100 has a first tooth 102 on the sideof an inner sleeve 36 and a second tooth 104 on the side of the cam robe38. The first tooth 102 protrudes integrally from an end portion of anoutside boss portion 48 of the inner sleeve 36, and can rotateintegrally with the camshaft 20. As shown in FIG. 14, the first tooth102 extends in the circumferential direction of the outside boss portion48, covering a region narrower than a semicircle of the outside bossportion 48 by an angle θ.

On the other hand, the second tooth 104 protrudes integrally from an endportion of a small-diameter cylindrical portion 54 of the cam robe 38,and rotates integrally with the cam robe 38 or an intake cam 24. Asshown in FIG. 15, the second tooth 104 is in the form of a circular archaving an inside diameter substantially equal to that of the first tooth102, and extends covering a semicircle of the small-diameter cylindricalportion 54.

As shown in FIGS. 14 and 15, the first tooth 102 of the device for thecylinder #2 is in a state such that its front end abuts against thesecond tooth 104 of the device 30' for the cylinder #1 with respect tothe rotating direction Ro of the camshaft 20, while the second tooth 104of the cylinder #2 is in a state such that its rear end abuts againstthe first tooth 102 of the device 30' for the cylinder #3.

The first tooth 102 of the device 30' for the cylinder #1 is omitted, asshown in FIG. 16, while the second tooth 104 of the device 30' for thecylinder #4 abuts in like manner against a second tooth 106 which ismounted on the camshaft 20, as shown in FIG. 11. This second tooth 106has the same shape and function as the first tooth 102.

The first and second teeth 102 (106) and 104 between the other adjacentdevices 30' and between the adjacent variable valve timing devices 32'on the side of the camshaft 22 are engaged in the same relation.

Since the variable valve timing devices 30' and 32' operate in the samemanner, the operation of the device 30' for the cylinder #2 will bedescribed below.

When the rotating speed of the engine 10' is in the low-speed rotationregion, a viscous coupling 40 of the device 30' allows relative rotationbetween the camshaft 20 (inner sleeve 36) and the intake cam 24 (camrobe 38), as mentioned before.

When the intake cam 24 depresses a roller 82 on a rocker arm 80 by meansof its lift face 24b as the intake cam 24 rotates, in this operatingstate of the engine 10', the intake cam 24 is subjected to the reactionforce from the roller 82 on the rocker arm 80, as mentioned before.Although the viscous coupling 40 allows relative rotation between thecamshaft 20 and the cam robe 38 in this case, however, the first tooth102 (106) on the side of the camshaft 20 and the second tooth 104 of thecam robe 38, which cooperate with each other, are in engagement, so thatthe camshaft 20 and the cam robe 38 rotate integrally with each other.Accordingly, an intake valve 86 lifts following the cam profile of theintake cam 24, thereby opening an intake port 90. The rise portion ofthe lift of the intake valve 86 in this case is represented by afull-line portion of a valve lift characteristic Hvl in FIG. 17.

When the rotation of the intake cam 24 advances so that a return face24d of the intake cam 24, following a cam top 24c, reaches the roller 82on the rocker arm 80, the intake cam 24 is subjected to the restoringforce of a valve spring 92 in its rotating direction through the roller82 on the rocker arm 80. Hereupon, the first tooth 102 (106) on the sideof the camshaft 20 and the second tooth 104 of the cam robe 38, whichcooperate with each other, allow a relative displacement such that theymove away from each other through the viscous coupling 40. The rotationof the intake cam 24 or the cam robe 38 with respect to the camshaft 20is consequently advanced by means of the restoring force of the valvespring 92. As this is done, the spiral spring 42 is elastically deformedin the direction opposite to the winding direction R1.

Accordingly, the valve closing timing of the intake valve 86 is earlierthan in the case where the camshaft 20 and the intake cam 24 rotateintegrally with each other. In this case, the fall portion of the liftof the intake valve 86 is represented by a broken-line portion of thevalve lift characteristic Hvl in FIG. 17. The valve closing timing ofthe intake valve 86 is advanced by a advanced angle A' in terms of therotation of the camshaft 20. This advanced angle A' increases to reachits maximum value Amax (e.g., 30°) as the rotating speed of the engine10' lowers, as mentioned before. FIG. 17 also shows the lift speedcharacteristic V1 of the intake valve 86. As seen from this lift speedcharacteristic V1, the valve closing speed of the intake valve 86increases.

While a base circle face 24a of the intake cam 24 is passing by theroller 82 on the rocker arm 80 after the intake valve 86 is closed, theintake cam 24 is restored to the initial rotational angle position withrespect to the camshaft 20 by means of the restoring force of the spiralspring 42.

When the rotating speed of the engine 10' is in the low-speed rotationregion, the valve-open period Tvl of the intake valve 86 is reduced by amargin corresponding to the advance of the valve closing timing thereof,although the valve opening timing of the intake valve 86 is constant, asmentioned before.

When the rotating speed of the engine 10' is in the high-speed rotationregion, on the other hand, the transmission torque of the viscouscoupling 40 increases in proportion to the rotating speed of the engine10', as mentioned before, so that it is difficult to allow the relativerotation between the camshaft 20 (inner sleeve 36) and the intake cam 24(cam robe 38).

In the case that the rotating speed of the engine 10' is in thehigh-speed rotation region, therefore, the intake cam 24 rotatessubstantially integrally with the camshaft 20, and the valve liftcharacteristic Hvh of the intake valve 86 is settled in accordance withthe cam profile of the intake cam 24 even at its fall portion, asindicated by full line in FIG. 17. In consequence, the valve-open periodTvh of the intake valve 86 is longer than the valve-open period Tvl forthe low-speed rotation region.

The variable valve timing devices 32' on the side of exhaust valves 94function in the same manner as the aforementioned devices 30'.

Thus, according to the devices 30' and 32' of the second embodiment,although the valve opening timings of the intake and exhaust valves 86and 94 are fixed in the whole operation region of the engine 10' by thefunction of the dog clutch 100, the valve closing timings of thesevalves vary depending on the rotating speed of the engine 10'. Morespecifically, although the valve-open periods Ti1 and Te1 of the intakeand exhaust valves 86 and 94 are reduced individually, as shown in FIG.18, when the rotating speed of the engine 10' is in the low-speedrotation region, these valve-open periods Ti2 and Te2 increase when therotating speed of the engine 10' is in the high-speed rotation region.

Referring to FIG. 19, there is shown a variable valve timing device 300according to a third embodiment which is applied to an intake valve 86.A cam robe 38 of this device 300 is mounted directly on a camshaft 20for rotation, and an annular groove 302 is formed on the innerperipheral surface of the cam robe 38 in a region corresponding to aneck portion 56. One end of each of a plurality of radial holes 304opens into the annular groove 302, and the respective other ends of theradial holes 304 opens on the outer peripheral surface of the neckportion 56 and are located in a same circle.

On the other hand, arcuate grooves are formed individually on therespective inner peripheral surfaces of a cam journal 60 and a cam cap62 which hold the neck portion 56 of the cam robe 38, these arcuategrooves form one circumferential groove 306 on which the other endopenings of the radial holes 304 face. A communication passage 308 isformed in the cam journal 60. One end of the communication passage 308is connected to the circumferential groove 306, while the other endthereof is connected to a lubricating oil supply channel (not shown) ina cylinder head. Thus, lubricating oil in this supply channel is fedinto the annular groove 302 through the circumferential groove 306 andthe radial holes 304, whereby the annular chamber 302 is filled with thelubricating oil.

The variable valve timing device 300 of the third embodiment, asdescribed above, unlike the device 30 of the first embodiment, does notrequire the metal bearing 52, so that the number of components of thedevice 300 is smaller. The lubricating oil in the annular chamber 302oozes out onto the respective sliding contact surfaces of the camshaft20 and the cam robe 38, and reduces wear of these sliding contactsurfaces.

Referring now to FIGS. 20 and 21, there is shown a variable valve timingdevice 400 according to a fourth embodiment which is applied to anintake valve 86. An inner sleeve 36 of this device 400 has an egg-shapedbulging portion 402 in place of the aforementioned flange 44, and a camrobe 38 has an outer casing 404 in place of the aforementionedlarge-diameter cylindrical portion 50. This outer casing 404 includes apair of side rings 406, 408 which hold the bulging portion 402 from bothsides thereof, and an intermediate ring 410 which surrounds the bulgingportion 402 externally. These rings are connected to the cam robe 38 bymeans of a plurality of connecting bolts 412. Inside seals 414 and 416are arranged between the cam robe 38 and the inner sleeve 36 and betweenthe side ring 406 and the inner sleeve 36, respectively. Outside seals418 are arranged between a cover 78 and the respective outer peripheralsurfaces of the side rings 406 and 408, individually.

As seen from FIG. 21, part of the inner peripheral surface of theintermediate ring 410 forms a circular arc with which the arcuatesurface of the bulging portion 402 is in sliding contact, and a space issecured between the remaining portion of the inner peripheral surfaceand the outer peripheral surface of the bulging portion 402. Thus, thebulging portion 402 can rotate with respect to the intermediate ring 410within the range of a rotational angle region W shown in FIG. 21.

A hole 419 is formed in the top portion of the bulging portion 402, andthis hole 419 extends in the radial direction of the bulging portion402. A vane 420 is slidably fitted in the hole 419, and a spring 422 isdisposed between the bottom of the hole 419 and the inner end of thevane 420. This spring 422 urges the vane 420 in a direction such thatthe vane 420 projects from the hole 419. Thus, the outer end of the vane420 abuts against the inner peripheral surface of the intermediate ring400, thereby dividing the space between the intermediate ring 410 andthe bulging portion 402 into a pair of liquid chambers 424 and 426.

The bulging portion 402 is formed with a communication passage 428 whichintersects with the lower part of the hole 419, and this communicationpassage 428 opens into the liquid chambers 424 and 426 at the oppositeends of the bulging portion 402. Thus, the liquid chambers 424 and 426are connected to each other by means of the communication passage 428.The liquid chambers 424 and 426 and the communication passage 428 arefilled with oil.

As shown in FIG. 20, a rim 430 is formed integrally on the outerperipheral edge of the side ring 406, and this rim 430 surrounds aspiral spring 42. As shown in FIG. 22, the spiral spring 42 has itsinner end fixed to an outside boss portion 48 of the inner sleeve 36 andits outer end fixed to the rim 430 of the side ring 406.

According to the variable valve timing device 400 of the fourthembodiment described above, the rotation of an engine or a camshaft 20is transmitted from the bulging portion 402 of the inner sleeve 36 tothe outer casing 404 or the cam robe 38 through the oil in the oneliquid chamber 424. As this is done, the bulging portion 402 pressurizesthe oil in the liquid chamber 424, whereby the oil in the liquid chamber424 flows out into the liquid chamber 426 through the communicationpassage 428. In this case, the inner sleeve 36 and the cam robe 38 areallowed to relatively rotate with respect to each other. When the oilflows through the communication passage 428, the oil pressure in thehole 419 also increases, so that this oil pressure further presses thevane 420 against the inner peripheral surface of the intermediate ring410, so that the vane 420 securely separates the liquid chambers 424 and426.

When a lift face 24b of the intake cam 24 depresses a roller 82 on arocker arm 80 as the camshaft 20 rotates, the intake cam 24 is subjectedto a reaction force from the rocker arm 80, based on the urging force ofa valve spring 92. This reaction force acts so as to delay the rotationof the cam robe 38 or the intake cam 24 compared with the camshaft 20,as mentioned before. When the rotating speed of the camshaft 20 is inthe low-speed rotation region, enough time is secured for the outflow ofthe oil from the liquid chamber 424 into the liquid chamber 426, and thebulging portion 402 of the inner sleeve 36 and the outer casing 404relatively rotate to each other while subjecting the spiral spring 42 toelastic deformation, as shown in FIG. 23. As a result, the intake cam 24rotates with a delay behind the camshaft 20, so that the valve openingtiming of the intake valve 86 is delayed.

When the rotation of the camshaft 20 advances so that a return face 24dof the intake cam 24 reaches the roller 82 on the rocker arm 80,thereafter, the intake cam 24 is subjected to the restoring forces ofthe valve spring 92 and the spiral spring 42 in its rotating direction,as mentioned before. In this case, the rotation of the intake cam 24consequently advances with respect to the camshaft 20 with the oil inthe liquid chamber 426 flowing out into the liquid chamber 424. In theend, the state of FIG. 21 is restored from the state of FIG. 23, and thevalve closing timing of the intake valve 86 is advanced.

When the rotating speed of the engine or the camshaft 20 increases fromthe low-speed rotation region, enough time cannot be secured for thedelivery of the oil between the liquid chambers 424 and 426. As therotating speed of the camshaft 20 increases, both the delay of the valveopening timing of the intake valve 86 and the advance of the valveclosing timing are therefore reduced.

When the rotating speed of the camshaft 20 is in the high-speed rotationregion, the camshaft 20 and the intake cam 24 rotate integrally witheach other, and the valve opening and closing timings of the intakevalve 86 are settled in accordance with the cam profile of the intakecam 24.

Thus, also in the case of the variable valve timing device 400 of thefourth embodiment, the valve-open period Tv1 of the intake valve 86obtained when the rotating speed of the engine is in the low-speedrotation region is shorter than the valve-open period Tvh for thehigh-speed rotation region, as seen from the valve lift characteristicsHvl and Hvh in FIG. 24.

Referring to FIG. 25, there is shown a variable valve timing device 500according to a fifth embodiment which is applied to an intake valve 86.This device 500 differs from the device 400 of the fourth embodimentonly in that the open end of a communication passage 428 on the side ofa liquid chamber 426 is tapered. According to the device 500 of thefifth embodiment, the oil can flow out more easily from the liquidchamber 426 to a liquid chamber 424 than from the liquid chamber 424 tothe liquid chamber 426. When the rotating speed of an engine is in thelow-speed rotation region, therefore the valve closing timings of intakeand exhaust valves are further advanced, as seen from a valve liftcharacteristic Hvl' in FIG. 26. In consequence, as shown in FIG. 27, avalve-open period Tv' for the case of the fifth embodiment, comparedwith a valve-open period Tv for the case of the fourth embodiment, isfurther shorter when the rotating speed of the engine is in thelow-speed rotation region.

Referring to FIGS. 28 and 29, there is shown a variable valve timingdevice 600 according to a sixth embodiment which is applied to an intakevalve 86. In the case of this device 600, an inner sleeve 36 is formedintegrally with three first walls 602 on its outer peripheral surface,and these first walls 602 are arranged at regular intervals in thecircumferential direction of the inner sleeve 36. Meanwhile, alarge-diameter cylindrical portion 50 of a cam robe 38 is formedintegrally with three second walls 604 on its inner peripheral surface.These second walls 604 are arranged at regular intervals in thecircumferential direction of the large-diameter cylindrical portion 50,and are situated individually between the first walls 602. The firstwalls 602 and the second walls 604 are arranged alternately in thecircumferential direction of a camshaft 20.

Each of the first walls 602 is connected to the second wall 604, whichis situated on opposite sides with respect to the circumferentialdirection of the camshaft 20, by means of a front elastic member 608 anda rear elastic member 610. These elastic members 608 and 610 are hollow,and have liquid chambers 612 and 614 defined therein.

The liquid chamber 612 of the front elastic member 608 is connected to acollecting passage 616 by means of a passage 614 in the second wall 604.This collecting passage 616 is formed in the large-diameter cylindricalportion 50, and extends covering the whole circumference of thelarge-diameter cylindrical portion 50 in the circumferential directionthereof. The liquid chamber 614 of the rear elastic member 610 isconnected to a collecting passage 620 by means of a passage 618 in thesecond wall 604. This collecting passage 620, like the collectingpassage 616, is formed in the large-diameter cylindrical portion 50. Asshown in FIG. 28, however, the collecting passages 616 and 620 aresituated separately in the axial direction of the large-diametercylindrical portion 50.

As shown in FIG. 30, the collecting passages 616 and 620 are connectedto each other by means of a communication passage 622 formed in one ofthe second walls 604, and an orifice 624 is formed in the middle of thecommunication passage 622. The liquid chambers 612 and 614 and thepassages 614, 616, 618 and 620 are filled with oil.

According to the variable valve timing device 600 of the sixthembodiment, the rotatory force of the camshaft 20 is transmitted fromthe first walls 602 of the inner sleeve 36 to the second walls 604 ofthe large-diameter cylindrical portion 50 through the front elasticmembers 608, whereby the cam robe 38 or an intake cam 24 is rotated.

Thus, the liquid chamber 612 of the front elastic member 608 and theliquid chamber 614 of the rear elastic member 610 correspond to theliquid chambers 424 and 426 (see FIG. 21) of the device of the fourthembodiment, respectively. In consequence, the device 600 of the sixthembodiment, like the device 400 of the fourth embodiment, is arranged sothat the valve opening timing and valve closing timing of the intakevalve 86 is delayed and advanced, respectively, when the rotating speedof the engine is in the low-speed rotation region.

In this case, the delay of the valve opening timing is obtained bysubjecting the front elastic members 608 to an elastic deformation suchthat their corresponding liquid chambers 612 are reduced in capacityand, on the other hand, subjecting the rear elastic members 610 to anelastic deformation such that their corresponding liquid chambers 614are increased in capacity, as shown in FIG. 31, as the oil flows outfrom the liquid chambers 612 to the liquid chambers 614. In contrastwith this, the advance of the valve closing timing is obtained when thestate of FIG. 29 is restored from the state of FIG. 31 as the oil flowsout from the liquid chambers 614 to the liquid chambers 612.

The delay of the valve opening timing and the advance of the valveclosing timing can be adjusted by suitably setting the opening of theorifice 624 of the communication passage 622.

When the rotating speed of the engine is in the high-speed rotationregion, on the other hand, the delivery of the oil between the liquidchambers 612 and 614 is prevented substantially, and the valve openingtiming and valve closing timing of the intake valve 86 are settledindividually in accordance with the cam profile of the intake cam 24.Thus, the device 600 of the sixth embodiment has the valve liftcharacteristics Hvl and Hvh shown in FIG. 24.

Referring to FIG. 32, there is shown a variable valve timing device 700according to a seventh embodiment which is applied to an intake valve86. In this device 700, an inner sleeve 36 and a large-diametercylindrical portion 50 have one first wall 602 and one second wall 604each, and these first and second walls 602 and 604 are connected to eachother by means of one front elastic member 608 and one rear elasticmember 610. In this case, a passage 614 extending from a liquid chamber612 of the front elastic member 608 and a passage 616 extending from aliquid chamber 614 of the rear elastic member 610 are connected to eachother by means of a communication passage 702, and this communicationpassage 702 is provided with an orifice 624.

Although the variable valve timing device 700 has a simpler constructionthan that of the device 600 of the sixth embodiment, the device 700 hasthe same function as the device 600.

Referring to FIG. 33, there is shown part of a variable valve timingdevice 800 according to an eighth embodiment. This device 800 differsfrom the sixth embodiment in that the orifice 624 of the device 600 ofthe sixth embodiment is replaced with a variable orifice 802.

The variable orifice 802 is provided with a cylinder portion 804 whichis formed in a second wall 604 of a large-diameter cylindrical portion50, and this cylinder portion 804 extends in the diametrical directionof the large-diameter cylindrical portion 50 and intersects with acommunication passage 622. Opposite ends of the cylinder portion 804open in the outer peripheral surface of the large-diameter cylindricalportion 50 and the outer surface of the second wall 604 through a pairof vent holes 806, individually. A piston 808 is fitted in the cylinderportion 804, and a spiral groove 810 is formed on the outer peripheralsurface of the piston 808. This spiral groove 810 is situated in thecentral portion of the piston 808 with respect to the axial directionthereof. A compression coil spring 812 is located between the outer endof the cylinder portion 804 and the piston 808. This compression coilspring 812 presses the piston 808 inward in the diametrical direction ofthe large-diameter cylindrical portion 50, thereby exposing the spiralgroove 810 of the piston 808 to the communication passage 622.

According to the variable valve timing device 800 of the eighthembodiment, when the rotating speed of an engine or a camshaft 20increases, the piston 808 is subjected to a centrifugal force, and movestoward the outer end of the cylinder portion 804, resisting against theurging force of the compression coil spring 812, as shown in FIG. 34.This movement of the piston 808 reduces the opening of the variableorifice 802 by a margin corresponding to the length of exposure of thespiral groove 810 to the communication passage 622, as shown in FIG. 35.Since the opening of the variable orifice 802 is reduced as the rotatingspeed of the camshaft 20 increases, the flow of oil between liquidchambers is consequently retarded, so that the delay of the valveopening timing of an intake valve 86 and the advance of the valveclosing timing thereof are reduced individually.

Referring to FIG. 36, there is shown part of a variable valve timingdevice 900 according to a ninth embodiment. This device 900 is providedwith a solenoid 902 for driving the piston 808 of the aforementionedvariable orifice 802. This solenoid 902 can freely adjust the distanceof movement of the piston 808, that is, the opening of the variableorifice 802.

Referring to FIG. 37, there is shown a variable valve timing device 1000according to a tenth embodiment which is applied to an intake valve 86.This device 1000, like the aforementioned device 400 of the fourthembodiment, is arranged so that a space between an intermediate ring 410and a bulging portion 402 is divided into two chambers by means of avane 420. One of the two chambers is formed as a liquid chamber 1002,and the other is formed as an atmosphere chamber 1004. Thus, in the caseof the device 1000, the communication passage 428 connecting the liquidchambers 424 and 426 is not necessary.

The liquid chamber 1002 opens to the outside of an outer casing 404through a passage 1006 which is formed in the intermediate ring 410 anda cover 78, and an orifice 1008 is formed in the middle of the passage1006. This orifice 1008 may be replaced with the aforementioned variableorifice. On the other hand, the atmosphere chamber 1004 opens to theoutside of the outer casing 404 through a passage 1010 which is formedin the intermediate ring 410 and the cover 78.

Moreover, an axial passage 1012 is formed in a camshaft 20, and thisaxial passage 1012 is connected to the liquid chamber 1002 through apassage 1014 which is formed in the camshaft 20 and the bulging portion402. Also, the axial passage 1012 is connected to an oil supply passage(not shown), and this supply passage serves continually to feed oil intothe liquid chamber 1002 through the axial passage 1012.

Although the device 1000 of the tenth embodiment, unlike the foregoingembodiments, has only one liquid chamber, it can fulfill the samefunction as the device 400 of the fourth embodiment.

We claim:
 1. A valve drive system of an internal combustion engine,comprising:a first rotating member which rotates in association with acrankshaft of the internal combustion engine; a second rotating memberrotatable relatively to the first rotating member; a cam provided onsaid second rotating member and rotating integrally with the secondrotating member, thereby opening and closing a valve of said internalcombustion engine, in cooperation with a valve spring; and a connectingunit which connects said first rotating member and said second rotatingmember while permitting a relative rotation therebetween, saidconnection unit having a transmission unit which transmits the rotaryforce of said first rotating member to said second rotating member, anda varying unit which changes a rotation speed of said second rotatingmember with respect to said first rotating member in conjunction with arestoring force of said valve spring in accordance with an operationalstate of said internal combustion engine to determine a time oftermination of said valve opening with respect to the rotational phaseof said crankshaft, said connecting unit including a fluid couplingconnecting said first and second rotating members, said fluid couplingincluding,a fluid chamber defined between said first and second rotatingmembers, said fluid chamber having a viscous fluid sealed therein, afirst plate located in said fluid chamber and fixed to said firstrotating member, and a second plate located opposite said first plate insaid fluid chamber and fixed to said second rotating member.
 2. A valvedrive system of an internal combustion engine according to claim 1,wherein said fluid coupling changes a time of termination of a cam liftin accordance with the rotating speed of said internal combustionengine.
 3. A valve drive system of an internal combustion engineaccording to claim 2, wherein said second rotating member has a hollowsection which surrounds said first rotating member.
 4. A valve drivesystem of an internal combustion engine according to claim 3, whereinsaid internal combustion engine includes a plurality of cylinders, andsaid first rotating member being common to all of said plurality ofcylinders and said second rotating member being provided for each ofsaid cylinders.
 5. A valve drive system of an internal combustion engineaccording to claim 2, wherein said connecting unit further includes apusher portion provided in said first rotating member and a receivingportion provided in said second rotating member, said receiving portionengages said pusher portion in a process of opening said valve.
 6. Avalve drive system of an internal combustion engine according to claim5, wherein said connecting means further includes urging means forurging said first and second rotating members in a rotating directionsuch that said pusher portion abuts against said receiving portion.
 7. Avalve drive system of an internal combustion engine according to claim1, wherein said connecting unit decreases opening speed of said valve.8. A valve drive system of an internal combustion engine according toclaim 1, wherein said connecting unit increases closing speed of saidvalve.
 9. A valve drive system of an internal combustion engineaccording to claim 2, wherein said fluid coupling transmits the rotaryforce of said first rotating member to said second rotating member in aprocess of opening said valve.
 10. A valve drive system of an internalcombustion engine according to claim 9, wherein said connecting unitfurther includes urging means for urging said second rotating membertoward said first rotating member, the urging means maintains a constantrotational angle position of said second rotating member with respect tosaid first rotating member when said first rotating member and secondrotating member rotate integrally with each other.
 11. A valve drivesystem of an internal combustion engine according to claim 10, whereinsaid connecting means further includes limiting means for limiting theallowable range of relative rotation between said first and secondrotating members.
 12. A valve drive system of an internal combustionengine according to claim 10, wherein the urging means has a spiralspring.
 13. A valve drive system of an internal combustion engineaccording to claim 9, wherein said second rotating member includes afirst portion fitted on said first rotating member and a second portionhaving a diameter larger than the diameter of the first portion, thesecond portion constituting part of a casing which defines said fluidchamber.
 14. A valve drive system of an internal combustion engineaccording to claim 13, wherein said connecting unit includes a pusherportion provided in said first rotating member and a receiving portionprovided in said second rotating member, said receiving portion engagessaid pusher portion in a process of opening said valve, said secondportion being formed on one end of said second rotating member and saidreceiving portion formed on the other end portion of said secondrotating member.